This invention relates to a system and method for controlling the spindle of an electric motor, and more particularly to a system and method for controlling the spindle of a motor that rotates the platter of a disk drive.
Controlling the speed at which the platter of a disk drive rotates is very important, particularly as storage densities increase and platter size decreases. Thus, in a microdrive—i.e., a drive having a platter diameter of about 1 inch or less—even a small error in angular position may result in an incorrect sector being read or written.
One source of error in angular position is jitter resulting from irregularities in motor speed. One source of jitter is a mismatch between the motor drive profile, which is the voltage pattern applied to drive the motor, and the motor itself. One common type of motor used in a disk drive is a three-phase motor having four or six poles, which ideally has a sinusoidal drive profile. Such a motor commonly is driven with a drive profile that is known as a “trapezoidal” profile, which approximates a sinusoidal profile. However, because it only approximates a sinusoidal profile, a trapezoidal drive profile can result in motor speed irregularities—i.e., jitter or “torque ripple.” Moreover, a trapezoidal drive profile cannot take into account variations of a motor from an ideal motor.
It therefore would be desirable to be able to provide a motor drive profile that minimizes jitter.